The present invention relates to a fluid rotary apparatus, and more particularly to a fluid rotary apparatus suitable for allowing a vacuum pump to generate a vacuum in a wide range of vacuum pressures by discharging gas from a vacuum chamber installed in an apparatus for manufacturing semiconductors.
A vacuum pump for generating a vacuum environment is required by a CVD apparatus, a dry etching apparatus, a sputtering apparatus, an evaporating apparatus and the like for use in processes for manufacturing semiconductors. The vacuum pump is used also in processes of manufacturing magnetic disks and liquid crystal displays.
In recent years, a vacuum pump having a high operational performance has been more and more strongly demanded. In processes for manufacturing semiconductors, it has become desirable for circuits to be more and more highly integrated, for wafers to have larger diameters, for circuits to have large three-dimensional configurations, and for many kinds of semiconductors to be manufactured in small quantities. For high integration, clean equipment is required. Small equipment is necessary to provide wafers with large diameters. The equipment requires complex processing in multiple chambers so that the circuits can be large in three-dimensions. In order to manufacture many kinds of semiconductors in small quantities, equipment must have a network.
In order to comply with the above demands, it is necessary to prevent the vacuum pump from being polluted by oil, that the vacuum pump can generate a wide range of vacuum pressures, that the vacuum pump is corrosion-resistant, and that the vacuum pump has a high efficiency relative to the space it occupies.
Above all, the vacuum pump is required to generate vacuum pressures in a wide range. Although vacuum pressures as low as 10.sup.-8 to 10.sup.-10 torr have been required in recent years, one vacuum pump is incapable of generating such a high vacuum (i.e. low pressure). That is, in a positive displacement vacuum pump called a roughing rotary pump, two rotors synchronously rotate with a screw formed on the peripheral surface of each rotor engaging each other to generate a volume change in a closed space disposed between the screws. Gas is inhaled and compressed repeatedly to discharge the gas from the vacuum chamber by utilizing the volume change. This type of pump is suitable for discharging gas in the region of viscous flow, the pressure of which is near atmospheric pressure, but the pump operates in a pressure range from as high as atmospheric pressure to 10.sup.-3 torr. In a kinetic vacuum pump called a turbo pump, one rotor imparts momentum to gas molecules by its rotation so that the gas molecules are transferred by the momentum. As a result, gas is discharged from the vacuum chamber. The pump provides a vacuum pressure as low as 10.sup.-2 to 10.sup.-10 torr, but in principle, the pump is capable of discharging gas from the vacuum chamber in a molecular flow region, the vacuum pressure of which is lower than 10.sup.-1 torr and higher than 10.sup.-3 torr. In order to obtain a low vacuum pressure of 10.sup.-8 to 10.sup.-10 torr, it is necessary that a vacuum pressure of 10.sup.-2 to 10.sup.-3 torr is generated by the rotary pump such that a predetermined high (i.e. low pressure) vacuum is obtained by the turbo pump.
The use of two types of vacuum pumps leads to the installation of large equipment. That is, in order for equipment to carry out composite processing in multiple chambers, each chamber is required to be equipped with a vacuum apparatus. The use of two types of vacuum pumps for each chamber does not allow a vacuum discharge apparatus to be compact. Consequently, a space cannot be efficiently used and, in addition, the cost of equipment is high.